The general objective of this project is to study receptor mechanism related to the development of supersensitivity by arteries to Alpha-agonists during mineralocorticoid salt hypertension. The aorta from control rats and rats made hypertensive with infusion of aldosterone will be used for pharmacologic studies and radioligand binding assays. The functional studies will focus on dose-dependent changes in 42K and 45Ca effluxes, and contraction. The ligand binding measures will use 3H-prazosin and 3H-yohimbine. It is planned to compare parameters derived from each approach and to test the general hypothesis that sup]ersensitivity in aldosterone hypertension is related to increased concentration of Alpha-1 receptors. The specific aims deal with the determination of: (1) dissociation constants, KB, for prazosin and yohimbine based on analyses of competitive antagonism of agonist effects on isotope fluxes from intact aorta; (2) dissociation constant, KD, and maximum binding B max, for 3H-prazosin and 3H-yohimbine based on analyses of ligand saturation curves for membranes isolated from aorta; (3) relative potency series for Alpha-1 and Alpha-2 agonists based on ED50 from 42K efflux analyses and on Ki from competitive inhibition of radioligand binding; (4) receptor affinity, KA, and accupancy base on analyses of the effects of non competitive blockade by dibenamine; and (5) receptor kinetics by comparison of rate constants for the change in aortic 42K efflux indiced by norepinephrine in the presence of prazosin, with the rate of dissociation of 3H-prazosin from membrane receptors in the presence of norepinephrine. Comparison will be made between control and aldosterone hypertensive groups to test our hypotheses concerning the development of supersensitivity and its role in the pathogenesis of hypertension.